1. Field of the Invention
This invention relates to an electrophotographic light-receiving member having a sensitivity to electromagnetic waves such as light (which herein refers to light in a broad sense and indicates ultraviolet rays, visible rays, infrared rays, X-rays, xcex3-rays, etc.).
2. Related Background Art
In the field of image formation, photoconductive materials that form light-receiving layers of light-receiving members are required to have properties as follows: They are highly sensitive, have a high SN ratio [light current (Ip)/dark current (Id)], have absorption spectra suited to spectral characteristics of electromagnetic waves to be radiated, have a high response to light, have the desired dark resistance and are harmless to human bodies when used. In particular, in the case of light-receiving members set in electrophotographic apparatus used as business machines in offices, the safety in their use is important.
Photoconductive materials having good properties in these respects include amorphous silicon hydrides. For example, U.S. Pat. No. 4,265,991 discloses its application in electrophotographic light-receiving members.
In the production of such light-receiving members, it is common to form photoconductive layers comprised of amorphous silicon, by film forming processes such as vacuum deposition, sputtering, ion plating, heat-assisted CVD, light-assisted CVD and plasma-assisted CVD, which layers are formed on conductive supports while heating the supports at 50xc2x0 C. to 350xc2x0 C. In particular, their production by plasma-assisted CVD is preferable and has been put into practical use. This plasma-assisted CVD is a process in which material gases are decomposed by high-frequency or microwave glow discharging to form amorphous silicon deposited films on the conductive support.
U.S. Pat. No. 5,382,487 discloses an electrophotographic light-receiving member having a photoconductive layer formed of amorphous silicon containing halogen atom. This publication reports that incorporation of 1 to 40 atom % of halogen atoms into amorphous silicon enables achievement of a high thermal resistance, and also electrical and optical properties preferable for a photoconductive layer of an electrophotographic light-receiving member.
Japanese Patent Application Laid-open No. 57-115556 discloses a technique in which a surface barrier layer formed of a non-photoconductive amorphous material containing silicon atoms and carbon atoms is provided on a photoconductive layer formed of an amorphous material mainly composed of silicon atoms, in order to achieve improvements in electrical, optical and photoconductive properties such as dark resistance, photosensitivity and response to light and service environmental properties such as moisture resistance and also in stability with time. Japanese Patent Application Laid-open No. 60-67951 also discloses a technique concerning a photosensitive member superposingly provided with a light-transmitting insulating overcoat layer containing amorphous silicon, carbon, oxygen and fluorine. Japanese Patent Application Laid-open No. 62-168161 discloses a technique in which an amorphous material containing silicon atoms, carbon atoms and 41 to 70 atom % of hydrogen atoms as constituents is used to form a surface layer.
Japanese Patent Application Laid-open No. 58-21257 discloses a technique in which support temperature is changed in the course of the formation of a photoconductive layer and inhibition bandwidth is changed in the photoconductive layer to thereby obtain a photosensitive member having a high resistance and a broad photosensitive region. Japanese Patent Application Laid-open No. 58-121042 discloses a technique in which energy gap state density is changed in the direction of layer thickness of a photoconductive layer and the energy gap state density of a surface layer is controlled to be 1017 to 1019 cmxe2x88x923 to thereby prevent surface potential from being reduced because of humidity. Japanese Patent Application Laid-open No. 59-143379 and No. 61-201481 disclose a technique in which amorphous silicon hydrides having different hydrogen contents are superposingly formed to obtain a photosensitive member having a high dark resistance and a high sensitivity.
Japanese Patent Application Laid-open No. 58-88115 discloses that, aiming at an improvement in image quality of an amorphous silicon photosensitive member, atoms of Group III of the Periodic Table are incorporated in a large quantity on the support side of a photoconductive layer. Japanese Patent Application Laid-open No. 62-83470 discloses a technique in which characteristic energy of an exponential tail of light absorption spectra is controlled to be not more than 0.09 eV in a photoconductive layer of an electrophotographic photosensitive member to thereby obtain high-quality images free of after-image development. Japanese Patent Application Laid-open No. 62-112166 also discloses a technique in which flow rate ratio of B2H6/SiH4 is maintained at 3.3xc3x9710xe2x88x927 or above to form a carrier transport layer to thereby make free of after-image development.
Further, Japanese Patent Application Laid-open No. 60-95551 discloses a technique in which, aiming at an improvement in image quality of an amorphous silicon photosensitive member, image forming steps of charging, exposure, development and transfer are carried out while maintaining temperature at 30 to 40xc2x0 C. in the vicinity of the surface of the photosensitive member to thereby prevent the surface of the photosensitive member from undergoing a decrease in surface resistance which is due to water absorption on that surface and also prevent smeared images from occurring concurrently therewith.
These techniques have achieved improvements in electrical, optical and photoconductive properties and service environmental properties of electrophotographic light-receiving members, and also have concurrently brought about an improvement in image quality.
The electrophotographic light-receiving members having a photoconductive layer comprised of an amorphous silicon material have individually achieved improvements in properties in respect of electrical, optical and photoconductive properties such as dark resistance, photosensitivity and response to light and service environmental properties and also in respect of stability with time, and running performance (durability). However, improvements are still unsatisfactory from an overall viewpoint, and there is room for further improvements to make overall properties better.
In particular, there has been rapid progress in making electrophotographic apparatus have higher image quality, higher speed and higher running performance, and the electrophotographic light-receiving members are required to be more improved in electrical properties and photoconductive properties and also to greatly improve their performances in every environment while maintaining chargeability and sensitivity. Then, as a result of improvements made on optical exposure devices, developing devices, transfer devices and so forth in order to improve image characteristics of electrophotographic apparatus, the electrophotographic light-receiving members are now also required to be more improved in image characteristics than ever before.
Under such circumstances, although the conventional techniques as noted above have made it possible to improve properties to a certain degree in respect of the subjects stated above, they still can not be said to be satisfactory in regard to the improvements in chargeability, sensitivity, response to light, and image quality. In particular, as the subjects for making amorphous silicon light-receiving members have much higher image quality, it has now been also sought to prevent variations of electrophotographic performances (e.g., chargeability and sensitivity) due to changes in surrounding temperature (i.e., improve service environmental properties) and to make photomemory such as blank memory and ghost occur less (i.e., improve photoconductive characteristics such as response to light).
For example, in order to prevent smeared images caused by amorphous silicon photosensitive members, a drum heater is provided inside a copying machine to keep the surface temperature of the photosensitive member at about 40xc2x0 C., as disclosed in Japanese Patent Application Laid-open No. 60-95551. In conventional photosensitive members, however, the dependence of chargeability on temperature, which is ascribable to formation of pre-exposure carriers or heat-energized carriers is so great that, in an actual service environment inside the copying machine, photosensitive members could not avoid being used in the condition wherein they have a lower chargeability than that originally possessed by the photosensitive members. For example, chargeability may drop by nearly 100 V in the state where the photosensitive members are heated to about 40xc2x0 C., compared with use at room temperature.
In the past, in the period (e.g., at night) when copying machines were not used, the drum heater was maintained under power so as to prevent the smeared images that are caused when ozone products formed by corona discharging of a charging assembly are adsorbed on the surface of a photosensitive member. Nowadays, however, it has become popular not to power the apparatus as far as possible when not in use e.g., at night, for the purpose of saving electric power. When copies are continuously taken without electrifying the drum heater, the surrounding temperature of the photosensitive member rises as a result of charging and so forth to make chargeability lower with a rise of temperature, causing a phenomenon that image density changes during copying.
When the same original is continuously and repeatedly copied, an after-image due to imagewise exposure in they previous copying step (called xe2x80x9cghostxe2x80x9d) may also occur on the image in the subsequent copying, or a density difference on copied images (called xe2x80x9cblank memoryxe2x80x9d) may occur because of the influence of blank exposure which is irradiation made on the photosensitive member at the paper feed intervals during the continuous copying in order to save toner. Such phenomena have been investigated to improve image quality.
Meanwhile, in recent years, computers have come into wide use in offices and ordinary homes, and electrophotographic apparatus are not only used as conventional copying machines but also are now sought to be made digital so that they can play a role as facsimile machines or printers. Semiconductor lasers and LEDs used as exposure light sources for digitizing image data are chiefly those having relatively long wavelengths ranging from near infrared light to red visible light in view of light emission intensity and cost. Hence, it has become desirable to solve problems on characteristics which have been not seen in conventional analog machines employing halogen light.
In particular, the fact that the relationship between the exposure value and the surface potential of photosensitive members, i.e., what is called E-V characteristics (E-V curves) may shift depending on temperature (i.e., temperature characteristics of sensitivity) and the fact that the linearity of the E-V characteristics (E-V curves) (i.e., linearity of sensitivity) may lower have now attracted notice as characteristic features in the case where semiconductor lasers or LEDs are used. More specifically, digital machines making use of semiconductor lasers or LEDs as exposure light sources have caused an additional problem that, when the photosensitive member temperature is not controlled by the drum heater mentioned above, the surrounding temperatures may cause a change in sensitivity because of a lowering of the linearity of sensitivity or the temperature characteristics of sensitivity, resulting in a change in image density.
Accordingly, in designing electrophotographic light-receiving members, it is required to achieve improvements from the overall viewpoints of layer configuration and chemical composition of each layer of the light-receiving members so that the problems as discussed above can be solved, and also to achieve a much more improvement in properties of the amorphous silicon materials themselves.
Accordingly, an object of the present invention is to solve the various problems caused in conventional electrophotographic light-receiving members having the light-receiving layer formed of amorphous silicon materials as stated above.
That is, an object of the present invention is to provide an electrophotographic light-receiving member that has superior electrical, optical and photoconductive properties, and is substantially always stable (having superior service environmental properties) almost without dependence of these properties on service environment, promising a superior image quality; in particular, to provide an electrophotographic light-receiving member that has achieved all the improvement in chargeability, the improvement in temperature characteristics thereof and the decrease in photomemory, and has been dramatically improved in image quality.
Another object of the present invention is to provide an electrophotographic light-receiving member that has been improved in the temperature characteristics of sensitivity and the linearity of sensitivity especially in the case where semiconductor lasers or LEDs are used as exposure light sources, and has been dramatically improved in image quality.
A still another object of the present invention is to provide an electrophotographic light-receiving member having a superior running performance, which may cause neither exposure fatigue nor any deterioration in repeated use.
To achieve the above objects, the present invention provides an electrophotographic light-receiving member comprising a conductive support and provided thereon a photoconductive layer formed of a non-single-crystal material mainly composed of silicon atom and containing at least one of hydrogen atom and halogen atom and at least one element belonging to Group IIIb of the periodic table; wherein the photoconductive layer has at least one of the hydrogen atom and the halogen atom in a content of from 10 atom % to 30 atom %, an optical band gap of from 1.75 eV to 1.85 eV and a characteristic energy obtained from the exponential tail of light absorption spectra, of from 55 meV to 65 meV, and has on the surface side thereof a second layer region that absorbs a prescribed amount of light incident on the photoconductive layer and on the support side thereof the other first layer region; the element belonging to Group IIIb of the periodic table being contained in the second layer region in an amount made smaller than that in the first layer region.
The present invention also provides an electrophotographic light-receiving member comprising a conductive support and provided thereon a photoconductive layer formed of a non-single-crystal material mainly composed of silicon atom and containing at least one of hydrogen atom and halogen atom and at least one element belonging to Group IIIb of the periodic table; wherein the photoconductive layer has at least one of the hydrogen atom and the halogen atom in a content of from 10 atom % to 20 atom %, an optical band gap of 1.75 eV or below and a characteristic energy obtained from the exponential tail of light absorption spectra, of 55 meV or below, and has on the surface side thereof a second layer region that absorbs a prescribed amount of light incident on the photoconductive layer and on the support side thereof the other first layer region; the element belonging to Group IIIb of the periodic table being contained in the second layer region in an amount made smaller than that in the first layer region.
The present invention still also provides an electrophotographic light-receiving member comprising a conductive support and provided thereon a photoconductive layer formed of a non-single-crystal material mainly composed of silicon atom and containing at least one of hydrogen atom and halogen atom and at least one element belonging to Group IIIb of the periodic table; wherein the photoconductive layer has at least one of the hydrogen atom and the halogen atom in a content of from 25 atom % to 35 atom %, an optical band gap of 1.80 eV or above and a characteristic energy obtained from the exponential tail of light absorption spectra, of 55 meV or below, and has on the surface side thereof a second layer region that absorbs a prescribed amount of light incident on the photoconductive layer and on the support side thereof the other first layer region; the element belonging to Group IIIb of the periodic table being contained in the second layer region in an amount made smaller than that in the first layer region.
The present invention further provides an electrophotographic light-receiving member comprising a conductive support and provided thereon a photoconductive layer formed of a non-single-crystal material mainly composed of silicon atom and containing at least one of hydrogen atom and halogen atom and at least one element belonging to Group IIIb of the periodic table; wherein the photoconductive layer has on the support side thereof a first layer region having at least one of the hydrogen atom and the halogen atom in a content of from 20 atom % to 30 atom %, an optical band gap of from 1.75 eV to 1.85 eV and a characteristic energy obtained from the exponential tail of light absorption spectra, of from 55 meV to 65 meV, and on the surface side thereof a second layer region having at least one of the hydrogen atom and the halogen atom in a content of from 10 atom % to 25 atom %, an optical band gap of from 1.70 eV to 1.80 eV and a characteristic energy obtained from the exponential tail of light absorption spectra, of 55 meV or below; the optical band gap in the second layer region being made smaller than that in the first layer region, and the element belonging to Group IIIb of the periodic table being contained in the second layer region in an amount made smaller than that in the first layer region.
The present invention still further provides an electrophotographic light-receiving member comprising a conductive support and provided thereon a photoconductive layer formed of a non-single-crystal material mainly composed of silicon atom and containing at least one of hydrogen atom and halogen atom and at least one element belonging to Group IIIb of the periodic table; wherein the photoconductive layer has on the support side thereof a first layer region having at least one of the hydrogen atom and the halogen atom in a content of from 25 atom % to 40 atom %, an optical band gap of from 1.80 eV to 1.90 eV and a characteristic energy obtained from the exponential tail of light absorption spectra, of 55 meV or below, and on the surface side thereof a second layer region having at least one of the hydrogen atom and the halogen atom in a content of from 10 atom % to 25 atom %, an optical band gap of from 1.70 eV to 1.80 eV and a characteristic energy obtained from the exponential tail of a light absorption spectrum, of 55 meV or below; the optical band gap in the second layer region being made smaller than that in the first layer region, and the element belonging to Group IIIb of the periodic table being contained in the second layer region in an amount made smaller than that in the first layer region.